With the rapid spread of digital cameras and portable audio players these days, there is an increasing demand for high-capacity nonvolatile semiconductor memory. In this connection, NAND flash memory (hereinafter, sometimes simply referred to as flash memory) has been widely used as nonvolatile semiconductor memory.
Furthermore, with the recent progress of semiconductor technology, the movement of NAND flash memory toward higher capacity is significant. The NAND flash memory has a NAND string structure where a plurality of memory cells are connected in series. As the NAND flash memory has higher capacity, the number of memory cells included in the NAND string also increases.
The conventional NAND flash memory has the following problem: as the number of memory cells in the NAND string increases, the operational reliability deteriorates.
The invention provides a method of writing data into semiconductor memory and a memory controller which are capable of improving the operational reliability.